Generally, a pump used for pumping a cryogenic fluid, such as liquefied natural gas (LNG), may include a hydraulically actuated piston pump. The hydraulically actuated piston pump may be hydraulically driven during a pumping stroke and may be spring driven during a return stroke of the pump. In such a situation, the spring may wear making it difficult to achieve consistent spring parameters over a service life of the spring.
For example, consistency in a spring force, spring stiffness, a travel distance of the spring, and/or other parameters of the spring may alter over the service life in turn affecting one or more pumping parameters of the pump. Also, for the cryogenic fluid, such as LNG, a movement of the piston of the pump may have to be controlled accurately during an end of the pumping stroke and/or a beginning of the return stroke in order to limit vaporization of the LNG during the pumping cycle.
In some situations, a hydraulically driven piston may be employed. However, in such situations, an efficiency of the pump may be decreased as a volume of a hydraulic fluid required during the return stroke in order to retract the piston may be same as a volume of the hydraulic fluid required to extend the piston during the pumping stroke. Also, a pressure of the hydraulic fluid may have to be controlled accurately during the pumping stroke and/or the return stroke in order to limit vaporization of the LNG during the pumping cycle.
U.S. Pat. No. 5,263,828 describes a two-cylinder thick matter pump having a hydro-controlled storage piston which is filled during thick matter feed with feed cylinders and evacuated by the hydro-controlled storage piston into a feed pipe between the strokes of feed pistons to reduce a pressure drop and an undelivered amount in the feed pipe. The hydro-control of the storage piston is served by a working piston to be acted upon hydraulically on both sides, that is controlled with the feed cylinders and whose limits of travel, with the limits of travel of the storage piston, are fixed on a storage driving cylinder when the storage driving cylinder is fully evacuated and is filled.